Catalytic muffler



June 26, 1962 E. J. HOUDRY 3,041,149

CATALYTIC MUFFLER Filed Aug. 7, 1958 2 Sheets-Sheet 1 Y INVENTOR. EUGENEJ. HOUDRY ATTORNEYS June 26, 1962 E. J. HoUDRY CATALYTIC MUFFLER 2Sheets-Sheet 2 Filed Aug. 7, 1958 FIG. 3A.

FIG. 4.

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EUGENE J. HouDRY ATTORNEYS ,innocuous products escape from the mufller.

3,041,149 Patented June 26, 1962 3,041,149 CATALYTEC MUFFLER Eugene J.Hendry, Ardmore, Pa., assignor to Oxy-Catalyst, Inc., Wayne, Pa., acorporation of; Pennsylvania Filed Aug. 7, 1958, Ser. No. 753,845

7 Claims. (Cl. 23--233) i This Vinvention relates to catalytic mufhersof the type designed to receive exhaust gases from an internalcombustion engine and effect oxidation of the unburned constituentsthereof. The term muffler is used not so much for its acousticproperties as for the fact that it is located in the position of anordinary muffler between the exhaust manifold of an engine and thetailpipe. In general, the apparatus ofthe type herein refer-red to doeshave theacoustic properties of suppressing noise to a considerabledegree though it may be augmented by additional mulfling means tofurther reduce noise.

While .the present invention has other uses, as will be apparenthereafter, it Irelates primarily to catalyticY muiilers for use onpassenger automobiles and trucks particularly when they utilize leadedgasolines. The general characteristics required for suc-h a muffler areset forth in my application, Serial No. 737,424, tiled May 23, 1958. lngeneral, they involve the use of catalysts in the form of small pelletswith the bed of such catalyst so arranged as to receive the exhaust`gases mixed with added air and presentingto such gases a properly.determined inlet area and thickness Vof bed in the direction of flow.When the various requirements are properly chosen, oxidation ofhydrocarbons as Well as carbon monoxide in the exhaust gases.` iseffected to a substantially complete extent with the result that onlyFurthermore, with proper design as set forth in said applications,conditions for quick starting and proper operation under the variousextremes of driving conditions are secured. In a muier of this type, thetemperature of the catalyst bed under normal operating conditionsvar-ies between l,O and l,2'00 F. While the requirements for properoperation may be achieved by many shapes and arrangements of catalyticbeds and containers therefore, modern automobiles and the necessity formaintaining low the costs of catalytic muiflers impose certain practicalrestrictions. For example, pasits ends by radial plate members. Thescreens referred to are desirably cylindrical, though this does notimply that they are necessarily circular cylinders. In fact, to minimizevertical height, and still provide the necessary volume andcross-sectional areas with respect to ilow,

A the cylindrical boundaries are desirably elliptical in crosssection,using the term elliptical to include such sections as may be derivedfrom horizontally elongated rectangles with some general rounding ofcorners and/or their faces. Irrespective of details of the configurationof the annular space, problems arise as follows:

The annular catalytic bed is necessarily, from -a practical standpoint,bounded or confined by metallic walls. Whatever metals may be used,their linear thermal coefficients of expansion are considerably inexcess of the corresponding linear coefficients of expansion of thecatalytic material of the bed. When the automobile is not in usethe'mufller will, of course, attain the ambient atmospherictemperatures. ln use, the bed temperature will rise to the order of1,200 F. and this will also be true to at least a partial degree of themetal enclosures. Letus assume, now, `some typical figures for acatalytic muffler for leaded gasoline applicable to. an averagepassenger automobile. Assuming a circular cylindrical configuration, theinner envelope of the bed may have a diameter of 4 inches, the outerenvelope a diameter of 6.4 inches, and the annular bed may have a lengthof about 30 inches. At atmospheric temperature, the volume of the bedspace would, therefore, be 587.5 cubic inches.l Let` it be assumed thatthis annular space is filled with catalyst. Assuming stainless steelv asthe matei rial used for the metal enclosure, if the temperature sengerautomobiles are presently being designed with less and lless clearanceof the ground and space, particularly in the vertical direction,available for a catalytic mufiler is substantially reduced. 'The hightemperatures of operation of a catalyst bed furthermore require heatinsulation for comfort and safety, stil-l further reducdifliculties areinvolved in other muflier constructions,

explanation will be facilitated by applying they discussion to acatalytic mufer design which is particularly satisfactory in the lightof the requirements of simplicity and space saving already mentioned.The most desirable form of the muler involves providing an annular bedof catalyst to the interior of which the gases are introduced and fromthe exterior of which they are exhausted, the catalyst bed being boundedinteriorly and exteriorly by perforated retaining screens and at `mostportion of the catalyst chamber.

rises to l,200 F., the volume of the catalyst space would increase toabout 606.5 cubic inches due to metal expansion, this representing anincrease in volume of 19 cubic inches. Y A

Meanwhile, the actual mass of the catalyst will increase by itsvolumetric expansion only about 5 cubic inches, the differencerepresenting a void of 14 cubic inches. The catalyst is a granular solidmaterial, and under the conditions of the rise of temperature justmentioned and vibration due to operation of the automobile, thecatalytic mass will act much like a liquid to settle down to a minimumvolume having itscenter of mass as low as possible. The

void of 14 cubic inches would thus occur at the upper- Unfortunately,however, this action, similar to that of a liquid, is not reversible,and under subsequent contraction of volume of the catalyst chamber thegranules will not ow back and rise to fill the chamber, but rather willact as a substantially rigid mass with resulting crushing ofthe catalystor permanent bulging of the enveloping metal. The result would be eitherimmediate destruction of the housing or the setting up of stresses whichwould ultimately lead to destruction. Furthermore, the remaining voidwould have a highly destructive effect on the catalyst and also lead toimproper operation. The gases flow at considerable velocity and thiswould lead to fluidization of the top layer of catalyst producingattrition between its granules leading to loss of the catalyst.Furthermore, in an annular arrangement, the space referred to wouldleave at the top of the bed a minimum length of path through the bed sothat an undue proportion of the gases would traverse this path leavingother portions of the catalyst relatively ineffective. Thisdeterioration of operation could be cured4 by feeding new catalyst intothe chamber from supply containers, but this solution would not cure thetrouble arising from compacting of the catalyst bed and consequentbulging or straining of the bounding walls. A further object of thepresent invention is, accordingly, to provide a solution to the problemarising from expansion and settling of the catalyst.- In brief,

this is accomplished by design of the catalytic muier to maintainsubstantially constant the geometric shape of the catalyst bed,permitting, while maintaining the shape, only such volumetric expansionas is characteristic of the catalyst itself. This end is achieved byproviding for an effective expansion of the catalyst chamber to avolumetric extent corresponding to the change of volume of the catalystwhile maintaining geometric similarity of Volumetric shape throughoutthe ranges of temperature changes involved.

Furthermore, in `accordance with the invention, the foregoing resultsare achieved without undue heat losses which might result if attemptswere made to solve the problems by cooling of the metal boundary walls.

Still other objects relate to the securing of shorter starting times andhigher temperature levels of the catalyst, thereby securing optimumperformance characteristics.

The foregoing and other objects of the invention particularly relatingto advantageous details of construction will become apparent from thefollowing description, read in conjunction with the accompanyingdrawings, in which:

FIGURE l is a vertical axial section through a preferredl form ofcatalytic muffler provided in accordance with the invention;

FIGURE 2 is a fragmentary section taken on the plane indicated atl2-2 inFIGURE 1;

FIGURES 3 and 3A are sections taken on the plane indicated at 3--3 inFIGURE 1 but showing aspects of this section under different operatingconditions;

FIGURE 4 is a side elevation of the muffler shown in the precedingfigures; and

-FIGURE 5 is a fragmentary axial section illustrating an alternativeembodiment of the invention.

Referring first to FIGURE 1, there is indicated at 2 the cylindricalouter metallic wall of the muffler. This wall may be a circular cylinderwhere such shape is permitted by space limitation requirements, or,where vertical space particularly is not available, the cylinder may beof elliptical or other oval configuration having a vertical dimensionless than its horizontal dimension in cross-section. For simplicity ofdescription in avoiding numerous references to such variation, thefollowing description will be in terms of circular cylindrical surfaces,

but with the understanding that the surfaces so referred to arenotnecessarily circular in cross-section but may be generally concentricoval or elliptical surfaces. The reference to cylindrical surfaces isalso not to be strictly construed since conical lor bulging surfaces maybe provided if desired. It will be evident, however, as the descriptionproceeds, that the same basic principles apply ywith such obviousmodifications of detailed dimensioning shoulders of annular formindicated at 18 and' 20 and al pair of inner shoulders of annular formindicated at 22 and 24. The right hand wall 8 is formed with an inwardlydirected conical portion 25. rThe central portion 26 of the wall 4 isprovided with a central opening into which is welded at Z8 the divergentdiffuser element 30 of a Venturi arrangement, this diffuser elementdesirably `opening at 32 in the right hand portion of the mufer body.The purpose of this is not only to save axial space but to effect byradiation from the catalyst bed preheating of the gases during theirpassage through the diffuser. The central portion of the right hand wall8 is closed as indicated at 34.

It may here be pointed out thatin an average type of muffler for use inconnection with passenger automobiles, the spacing between the walls 4and 8 may be of the order of 30 inches.

There is indicated at 36 the combustion gas exhaust pipe connected tothe exhaust manifold of 4the engine. This is secured by a flange 33 tothe central portion 26 of the end wall 4 by welding or bolting. The pipe36 is provided with converging wall elements 40 providing a nozzlespaced from the diffuser 30 at 42 and arranged to provide a jet of gasesinto the diffuser to carry air thereinto by ejector action from theannular space 44 connected by a tube `46 to the atmosphere, the airbeing drawn into the tube 46 from any desired location. This arrangementprovides for the additional air required for the oxidation of theunburned constituents of the engine exhaust gases.

`Bounding the internal surface of the wall 2 is a cylindrical heatinsulator 4S which may be of any conventional composition.

An internal bounding wall for the catalyst bed is provided by a screenmember 5G of cylindrical shape, this screen member being desirablyprovided by sheet metal having perforations therein which are lsmallerthan the catalyst pellets so as to retain them. The screen member Si) isheld in central position by the annular shoulders 22 and 24. At its endsand abutting the depressed portions 14 and 16 of the walls 4 and 8 itmounts annular heat insulating elements 52 and 54. An outer boundary forthe catalyst bed is provided by a screen member 56, also desirablyformed of sheet metal having perforations sufficiently small to preventescape of the catalyst pellets. The screen member 56 is held inannularly centered position by the shoulders 18 and 2f).

The catalyst mass is indicated at 58 and fills the annular space.between the screen members 50 and 56. This catalyst may be of the typedescribed in my prior applications referred to above and from themechanical standpoint may, for example, consist of particles in the formof short cylinders which typically may have a diameter of 1.5millimeters having somewhat random lengths of the same or largerdimensions. These catalyst particles are filled into the space betweenthe screen members Si) and 56 at random and the initial filling isdesirably effected with attendant vibration so as to compact theparticle mass and secure a maximum filling of the space with thecatalyst. The path of the exhaust gases, admixed with air in theVenturi, is from the space 69 within the screen member 50, through thescreen member Sti, -the catalyst bed, and the screen member 56, thenceinto the annular space 62 outside the screen member 56 and throughopenings 35 in the conical portion 25 of wall 8 into the interior of themember 12, where the hot gases may be directed over the air heating coil65, with final exhaust to the tailpipe 67. The provision of a heatingcoil y65 is in accordance with the disclosure of my application, SerialNo. 457,500, filed September 21, 1954, now abandoned.

As the operation of the catalyst proceeds, some is eventually lost byreason of attrition due to vibration producing a dust which escapesthrough the screen member 56 with gradual reduction of the amount ofcatalyst in the catalyst chamber provided between the screen lmembers 50and 56. It is highly desirable to keep the catalyst chamber full, and tothis end there are connected to the screen memberr 56 a plurality ofcatalyst supply chambers indicated at 66, 68 and 70 which communicatewith large openings in the screen member and extend outwardly throughthe insulation `48 and the wall 2 at the top thereof and are providedwith screw or other suitable caps -indicated at 74. These chambers arefilled with additional catalyst which, as catalyst is lost from thecatalyst chamber, will pass thereinto to maintain the same filled, beingdistributed therein by reason of vibration. The caps 74 may be removedfrom time to time to ascertain whether any additional catalyst should beadded. It may be here noted that the purpose of this addition'is not tofill upper voids such as were referred to in the beginning of thisspecification as possibly resulting from differential expansions. Aswill shortly appear,

the design is so made as to prevent the formation of such volumetricvoids.

At the bottom of the muiier there is desirably provided in communicationWith the catalyst chamber an outlet tube 72, normally capped, throughwhich the catalyst may be removed when its useful life has terminatedand relling of the muler is required.

Reference may now be made to those aspects of the invention relating tothe prevention of troubles due to ditferentialexpansions as outlinedabove.

As illustrated in FIGURE 2, the inner screen member 50 is not acontinuous cylinder but is provided with an expansion joint 76 involvingits overlapping edges 78 and '80. The -inner overlapping edge 78 isprovided along its length with a plurality of circumferentiallyelongated slots 82 which slidably receive the Shanks of rivets 3f-twhich are secured in 'or which loosely t circular openings in theoverlapping edge portion 80. A range of relative movement of the edgeportions is thus'provided, with the overlap Sil of suliicient extent toclose the slots throughout the range of movement. When the muffler iscold, the rivets project through the right hand ends of the slots `S2under the confinement by the shoulders 22 and 24 which determine thecylindrical surfacez aspect of the screen memberStl. As the temperaturerises, the attendant circumferential expansion of the screen member Stbcauses the overlapping edges to increase their overlap, and this ispermitted by the relative movements of the rivets 84 in their receivingslots `82, soy that at the highest operating temperature conditions willexist as illustrated yinl FIGURE 2. Thus, despite the changes oftemperature, the screen `50, which as a whole tends to expand by springaction, will present a substantially constant circumference tothecatalyst bed, the circumference being determined by the shoulders 22 and24.

Referring, now, to FIGURES 3 and 3A these show desirable to provide anexpansion joint on each side, and one of these will be described withthe understanding that the other is identical. i

In the case of `each of these joints there are provided the overlappinglongitudinally extending edges 88 and 9th As illustrated, the edge .90is diverted slightly outwardly to provide a shoulder 92. Rivets 4 spacedalong the overlapping edges are secured to the overlapping edge 90 andpass through corresponding circumferentially elongated slots 96 in theoverlapping edge 88, the overlapping edge 9) being of suicient length toclose these slots in all positions assumed during operation. Theelements forming the screen member 56 are so shaped that by springaction when the muffler is cold they tend to contract about theshoulders I8 and Ztl with the result that edges tend to increase theiroverlaps as indicated in FIG- URE 3. This overlap is limited by theshoulders 18 and 2b but there exists at 98 some clearance between therivet 94 and the lower end of the slot 96 in the case of each rivet. vThe reason for providing this clearance is that as operation of theengine is started the innermost portion of slots 96 will cause therivets to approach the upper ends of the slots 96. Nevertheless, thescreen members 56 will tend to approach by spring actions the shoulders13 and 2t), or, rather, bind upon the catalyst bed which may haveslightly expanded to prevent actual contact of the screen member withthese shoulders. Finally, to limit this spring action, the end of theoverlapping edge Sti-will ultimately abut the shoulder 22 whereupon thescreen member 56 effectively becomes a rigid cylinder thereafterexpanding at the rate determined by its own linear coefficient ofexpansion. This condition, however, is desirably attained only when thetemperature reaches its approximate maximum, and accordingly theexpansion then resulting is vso slight as to make negligible differenceof the expansion rates of the catalyst bed and the screen member 56 soas not to enlarge the catalyst space appreciably over the enlargement ofthe catalyst bed itself due to its own expansion. v

The axial expansion of the catalyst bed is readily accommodated by theflexibility of the end walls 4 and 3 which are insulated at 52 and 54from the catalyst bed so that they are subjected to a relatively smallrise of temperature, and this, in particular, prevents any greatincrease of the spaces between the shoulders 18 and 22 and between theshoulders Ztl and 24. The longitudinal `spacing between the inner facesof the insulators 52 and 54 will, of course, be changed to the extent ofexpansion of the wall 2 in an axial direction. However, this wallremains quite' cool due to the insulation 48, and for practical purposesit may be said that the axial length of the enclosure changes only to adegree corresponding to the change of axial length of the catalystbeddue to its own expansion. j

It will be noted that the Screen members 5t) and 56 have lengthssubstantially less than the spacings between the portions of walls 4 and8 which they might abut. They are accordingly free to expandlongitudinally without changing the volume of the catalyst space.

In the foregoing description it has been assumed that ordinary steel hasbeen used for the metal elements of the container and that this steel,as would ordinarily be the case, has expansion coetlicients considerablyexceeding corresponding coetlcients of the catalyst bed. Such ordinarysteel is desirably porcelainized for corrosion resistance. What has beendescribed so far, permits such use of ordinary steel with completeattainment of the objective of the invention which pertains to themaintenance of the geometric shape of the catalyst bed while permittinga proportional increase in linear dimensions in accordance with thethermal expansion of the bed. With ordinary steel,

however, this is attended by substantial movements of the expansionjoints in the screen members and 56 which will produce some relativesliding movements between these screen members and the catalystparticles, and may produce some shearing action particularly at theopenings in the screen members the edges of which may`have some cuttingaction on the catalyst. While this action does not appear to have anymajor deteriorating effect, it may be substantially completely avoidedby the adoption of addithe catalyst first becomes hot while the outerportion adjacent to the screen member is relatively cold. Somevolumetric expansion of the catalyst bed then takes place resulting inan increase of its outer diameter which may not be compensated by theincrease of circumference of the members forming the screen member 56.The clearance at'98 permits this expansion to take place against tionalprecautions by way of dimensioning and choice of metals so that therelative movements of the edges of the joints may be reduced to aminimum. Expedients to achieve this end will now be described, and itwill appear from the following that by the use of such expedients theremay even be eliminated the necessity for use of the expansion joints.

For example, if the insulation 48 is omitted (and for purpose of keepingthe muler from radiating` too much heat to the automobile Hoorinsulation is provided exterior to the nJvall 2), and it is assumed thatthe temperatures of the screen members 5t) and 55 and of the wall 2continuously approximate, during operating conditions, the catalyst bedtemperature, the screen member 50 might be made of stainless steelhaving a linear coeicient of expansion of l8 l06 per degree centigrade,and the screen member 56 and wall member 2` may be made of a steel suchas that containing 0.13% 'chromium and 2% nickel having a coeicient ofexpansion of 999x104, and without insulation at 52 and 54, and with -thetypical volumetric increase of the catalyst bed of the order of 1%between atmospheric temperature and the temperature of normal catalystoperation. The volume of the catalyst bed for the typical muierdimensions given above would approximately equal the volume of thecatalyst space through the range of temperature involved, the greaterincrease of diameter of the screen member 50 relative to the increase indiameter of the screen member 56, taking also into account the change inaxial dimension.

of the catalyst space effecting the compensation. The foregoing assumesthe same temperature for all of the metal parts, but taking into accountthe fact that the screen member 50 might have a higher temperature thanthe screen member 56 and this, in turn, a higher temperature than thewall 2, the same compensating aspects would be involved by a properchoice of the coeiiicients of expansion ofthe different metals formingthese various elements. The major aspect of this is, of course, that thecoefficient of expansion of the screen member 50 should be greater thanthe coeicient of expansion of the screen member 56.

Another solution to the same problem permits compensation by Vusingprimarily ordinary steel 'having a coetiicient of expansion of about 12106 for the screen member S6 and the wall 2, if stainless steel having acoefficient of expansion of 18x10-6 is used for screen member 5t?provided the diameter of the screen member S6 is properly chosen. Y Forexample, with the metals just indicated, and the other dimensions of themutiier as given above, the diameter of the screen member 56 could bechosen as 5.1 inches, here again the same temperatures being assumed forthe two screen members and the wall 2.

A third solution to the problem would involve the constructionillustrated in FIGURE 1 including the insulation 48 within the wall 2 tomaintain this wall at a low temperature while wall member 56 wasconstructed of ordinary steel, preferably porcelainized, with the screenmember 50 constructed of stainless steel of the type indicated. In thiscase, compensation would be effected by the maintenance of the wall 2 atrelatively low temperature.

FIGURE 5 shows still another solution in which the inner screen member50', corresponding to Sti, is corrugated at least longitudinally, andpreferably both longitudinally and circumferentialy but of ordinarysteel, the corrugations, by adding extra metal over a given provjectedarea, in eiect increasing the overall coeflicient of expansion, forexample, to that corresponding to an ordinary cylinder of stainlesssteel.

While the foregoing methods of compensation may be used without theyexpansion joints heretofore described it is desirable to use theexpansion jointsto take care of the transient conditions particularlyinvolved in starting up inasmuch as they may vary considerably from timeto time, producing unpredictable relative temperature variations of theparts of the muier. However, by utilizing the compensations involved invarious actual or effective coeiiicients of expansion of the metalparts, the relative movements in the expansion joints may be minimizedand 'thereby minimize destructive action on the catalyst particles.

It will be evident from the foregoing that there are attained thevarious objects of the invention above mentioned. The muffler comprisesa minimum number of parts readily assembled and accordingly the cost isa minimum. The chamber provided at 12 may not only contain a heater suchas indicated at 65 but may contain acoustic mufliing devices to minimizenoise.

It will be evident that various changes in details may be made withoutdeparting from the invention as defined in the following claims.

What is claimed is:

1. A catalytic muilier for the oxidation of combustible materials inengine exhaust gases comprising radially spaced inner and outer annularmembers provided with openings for iiow of gases, means closing the endsof the annular space between said members, catalyst particles withinsaid annular space, means for leading exhaust gases and excess oxygen tothe interior of said inner member, and means `for leading products ofoxidation by the catalyst from the exterior of said outer member, saidinner annular member having an eiective coefficient of expansion greaterthan the etective coefficient of expansion of said outer annular member,said effective coetiicients of expansion of said members being such thatas the container expands from a cold, non-operating condition tooperating temperatures, the volumetric thermal expansion of said annularspace is substantially equal to the volumetric thermal expansion of saidcatalyst particles within said annular space.

2. A catalytic mnier according to claim 1 in which the greater effectivecoefiicient of expansion of said inner annular member is provided bycorrugations.

3. A catalytic muier according to claim l in which said differentcoeiiicients of expansion are achieved by the use of ditierent materialsfor said annular members.

4. A catalytic muiiier according lto claim 1 in which said inner andouter annular members are provided with longitudinally extendingexpansion joints to permit circumlerential expansion in combination withmeans maintaining approximately constant the confining circumferences ofsaid members. v

5. A catalytic muiiier according to claim 2 in which said inner andouter annular members are provided with longitudinally extendingexpansion joints to permit circumferential expansion in combination withmeans maintaining approximately constant the confining circumferences ofsaid members.

6. A catalytic mufer according to claim 3 in which said inner and outerannular members are provided with longitudinally extending expansionjoints to permit circumferential expansion in combination with meansmaintaining approximately constant the confining circumferences of saidmembers.

7. A catalytic muier for the oxidation of combustible materials inengine exhaust gases comprising a container comprising radially spacedinner and outer members defining an annular space therebetween andprovided with openings for tlow of gases and means closing the ends ofthe annular space between said members, catalyst particles substantiallynlling the annular space of said containe'r, the volumetric thermalexpansion of the annular space of said container from a cold,non-operating condition to operating temperatures being substantiallyequal to the volumetric thermal expansion of the mass of catalystparticles in the annular space of said container, means for leadingexhaust gases and excess oxygen to the interior of Said inner member andmeans for leading products of oxidation by the catalyst from theexterior of said outer member.

7. A CATALYTIC MUFFLER FOR THE OXIDATION OF COMBUSTIBLE MATERIALS INENGINE EXHAUST GASES COMPRISING A CONTAINER COMPRISING RADIALLY SPACEDINER AND OUTER MEMBERS DEFINING AN ANNULAR SPACE THEREBETWEEN ANDPROVIDE WITH OPENINGS FOR FLOW OF GASES AND MEANS CLOSING THE ENDS OFTHE ANNULALR SPACE BETWEEN SAID MEMBERS, CATALYST PARTICLESSUBSTANTIALLY FILLING THE ANNULAR SPACE OF SAID CONTAINER, THEVOLUMETRIC THERMAL EXPANSION OF THE ANNULAR SPACE OF SAID CONTAINER FROMA COLD, NON-OPERATING CON-